David,

With the GLI installed the power output from the amp is noticeably lower, in
that I can barely hear the sound coming from the speakers. With the GLI not
installed the system is extremely loud (which will extend the period of time
I need to replace my holey muffler!). I agree that it seems like a ground
loop issue since the whining is eliminated by the GLI. Thinking that my
metal was not exposed enough, I sanded down the ground metal contact point
today but did not notice any improvement.. Good suggestion to ground both
amp and radio to same point...I'll give that a go.

Thanks,
Tracey